WDPN32 PGTW 091500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 25W (VAMCO) 
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 25W (VAMCO), LOCATED APPROXIMATELY 537 NM 
EAST-SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 
11 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED 
SATELLITE IMAGERY (EIR) INDICATES THAT THE SYSTEM IS STILL 
STRUGGLING TO CONSOLIDATE, WITH DEEP CONVECTION EXTENDING LINEARLY 
ACROSS THE SOUTHERN SEMICIRCLE OF THE OVERALL CIRCULATION AND WEAK 
SPIRAL BANDING EXPOSED TO THE NORTH, WRAPPING INTO THE OBSCURED LOW 
LEVEL CIRCULATION CENTER (LLCC). LATE RECEIPT OF 091157Z PARTIAL 
ASCAT-A AND 091311Z BULLSEYE ASCAT-B PASSES SHOW THAT, WHILE THE 
LLCC HAS CONSOLIDATED SIGNIFICANTLY OVER THE 12 HOURS SINCE THE 
PREVIOUS SCATTEROMETER PASS, IT IS STILL ELONGATED ALONG A SOUTHWEST-
NORTHEAST AXIS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE 
IN THE NORTHEAST POCKET OF THE AFOREMENTIONED ASCAT DATA. THE 
INITIAL INTENSITY IS SET AT 30 KTS WITH HIGH CONFIDENCE BASED ON 
MULTI-AGENCY DVORAK INTENSITY ESTIMATES OF T1.5-T2.0 (25-30 KNOTS) 
FROM PGTW AND RJTD, AND AN ADVANCED DVORAK TECHNIQUE (ADT) ESTIMATE 
OF T2.0. THE PREVIOUSLY MENTIONED ASCAT DATA LENDS SUPPORT TO THE 
INTENSITY ESTIMATE, AS THE ASCAT-B PASS IN PARTICULAR SHOWS A BROAD 
SWATH OF 30 KNOT WINDS EXTENDING FROM SOUTH TO NORTHEAST OF THE 
LLCC, THOUGH ONLY 20 KNOTS WRAPPING ALONG THE WESTERN PERIPHERY. TD 
25W IS TRACKING NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF A 
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST, THROUGH AN 
ENVIRONMENT WHICH IS VERY FAVORABLE FOR INTENSIFICATION WITH WARM 
(29-30 CELSIUS) SEA SURFACE TEMPERATURES (SST), LOW (5-10 KTS) 
VERTICAL WIND SHEAR (VWS), HIGH (120-140 KJ/CM^2) OHC AND STRONG 
EQUATORWARD AND MODERATE WESTWARD OUTFLOW. 
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. IN THE NEAR TERM, TD 25W WILL CONTINUE TO TRACK NORTHWESTWARD 
THROUGH TAU 12 BEFORE SLOWLY TURNING ONTO A WESTWARD TRACK BY TAU 36 
AS THE STR BUILDS AND EXTENDS TOWARDS THE WEST ROUGHLY ALONG THE 
25TH PARALLEL, EFFECTIVELY BLOCKING ANY FURTHER POLEWARD MOVEMENT. 
THE SYSTEM IS FORECAST TO CROSS LAMON BAY AND MAKE LANDFALL ALONG 
THE CENTRAL LUZON COAST DUE EAST OF MANILA NEAR TAU 60 BEFORE 
REEMERGING INTO THE OPEN WATERS OF THE SOUTH CHINA SEA BY TAU 72. 
WHILE THE SYSTEM HAS STRUGGLED TO CONSOLIDATE A WELL DEFINED 
CONVECTIVE CORE, IT IS EXPECTED THAT THE ENVIRONMENT SHOULD ALLOW 
FOR THIS CONSOLIDATION WITHIN THE NEXT 6 TO 12 HOURS RESULTING IN A 
RELATIVELY SLOW INTENSIFICATION THROUGH TAU 12. THEREAFTER, A 
COMBINATION OF RADIAL OUTFLOW, LOW VWS PROVIDED BY A DEVELOPING 
ANTI-CYCLONE OVER THE SYSTEM, AND PASSAGE OVER VERY WARM, HIGH OHC 
WATERS WILL ALLOW FOR STEADY INTENSIFICATION THROUGH TAU 24. A 
PERIOD OF RAPID INTENSIFICATION IS FORECAST BETWEEN TAUS 24 AND 48 
AS THE SYSTEM TRACKS OVER WATERS WITH HIGH OHC VALUES, VWS REMAINS 
VERY LOW AND THE UPPER-LEVEL ANTICYCLONE BECOMES VERTICALLY STACKED 
OVER THE LLCC, AND THE SYSTEM BEGINS TO TAP INTO A POLEWARD OUTFLOW 
CHANNEL. THE FORECAST CALLS FOR A PEAK INTENSITY OF 105 KNOTS AT TAU 
48, BUT ADDITIONAL INTENSIFICATION IS POSSIBLE PRIOR TO LANDFALL. AS 
THE SYSTEM CROSSES LUZON, INTERACTION WITH THE RUGGED TERRAIN WILL 
INDUCE SIGNIFICANT WEAKENING, WITH THE SYSTEM FORECAST TO REEMERGE 
INTO THE SOUTH CHINA SEA AS A MINIMAL TYPHOON. DYNAMIC TRACK 
GUIDANCE IS IN OVERALL GOOD AGREEMENT THROUGH THE TURN WESTWARD, 
WITH SOME SLIGHT DIFFERENCES IN THE SHARPNESS OF THE TURN LEADING TO 
A SPREAD OF 85NM AT TAU 48 THROUGH TAU 72, WITH NAVGEM DELINEATING 
THE POLEWARD EDGE OF THE ENVELOPE AND JGSM THE EQUATORWARD. THE 
TIGHT AGREEMENT IN THE MODEL SOLUTIONS LENDS OVERALL GOOD CONFIDENCE 
IN THE INITIAL PORTION OF THE JTWC FORECAST TRACK, LAID ON THE 
NORTHERN EDGE OF THE GUIDANCE ENVELOPE THROUGH TAU 48, THEN NEAR THE 
MULTI-MODEL CONSENSUS THROUGH TAU 72. INTENSITY GUIDANCE REMAINS 
MIXED, WITH A WIDE RANGE OF PEAK INTENSITIES BETWEEN ABOUT 65 KNOTS 
AND 90 KNOTS. HWRF REMAINS THE HIGH OUTLIER, BUT HAS COME DOWN A BIT 
TO 100 KNOTS PEAK. THE JTWC INTENSITY FORECAST IS HEDGED SLIGHTLY 
HIGHER THAN THE HWRF WITH FAIR CONFIDENCE.  
   C. AFTER TAU 72, THE SYSTEM WILL CONTINUE TO TRACK WESTWARD 
THROUGH TAU 120 UNDER THE STEERING INFLUENCE OF THE DEEP-LAYER STR 
TO THE NORTH. ONCE REEMERGING OVER THE OPEN WATERS OF THE SOUTH 
CHINA SEA, THE SYSTEM WILL REINTENSIFY TO A PEAK OF 70 KNOTS UNDER 
MARGINALLY FAVORABLE ENVIRONMENTAL CONDITIONS. NUMERICAL MODEL 
GUIDANCE DEPICTS INCREASING UNCERTAINTY AFTER TAU 72, WITH CROSS-
TRACK SPREAD INCREASING TO 250NM BY TAU 120. THE MAJORITY OF THE 
MODELS ARE TIGHTLY GROUPED NEAR THE MULTI-MODEL CONSENSUS, BUT A 
GROUPING OF THE NVGM, AFUM, AND UKMET ENSEMBLE CONTINUES TO TRACK 
THE SYSTEM NORTH-WESTWARD TOWARDS HAINAN ISLAND. WITH THE INCREASING 
UNCERTAINTY AND TWO DISTINCT GROUPINGS WITH INCREASINGLY DIVERGENT 
SOLUTIONS, THERE IS OVERALL LOW CONFIDENCE IN THE EXTENDED FORECAST 
TRACK, WHICH LIES JUST SOUTH OF THE MULTI-MODEL CONSENSUS.//
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